Fly balance organ. Coloured scanning electron micrograph (SEM) of the balance organ (haltere) of a fly (order Diptera). The haltere is the oval structure at centre and lower left. There are two of these organs in the dipterous insects. They are modified and reduced hindwings that help the insect sense its orientation and remain correctly balanced. Magnification: x258 when printed 10 centimetres wide.